U.S. patent number 9,580,562 [Application Number 14/186,135] was granted by the patent office on 2017-02-28 for adhesive compositions, adhesive articles and methods for making the same.
This patent grant is currently assigned to 3M Innovative Properties Company. The grantee listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Michael P. Daniels, Jay M. Jennen, James D. LaPerre, Scott R. Meyer.
United States Patent |
9,580,562 |
Daniels , et al. |
February 28, 2017 |
**Please see images for:
( Certificate of Correction ) ** |
Adhesive compositions, adhesive articles and methods for making the
same
Abstract
Adhesive compositions comprising a high molecular weight acrylic
copolymer and a low molecular weight copolymer are disclosed.
Adhesive articles and methods of making adhesive compositions and
articles are also described.
Inventors: |
Daniels; Michael P. (Inver
Grove Heights, MN), LaPerre; James D. (River Falls, WI),
Meyer; Scott R. (Woodbury, MN), Jennen; Jay M. (Forest
Lake, MN) |
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
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Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
38833767 |
Appl.
No.: |
14/186,135 |
Filed: |
February 21, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140171538 A1 |
Jun 19, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13546279 |
Jul 11, 2012 |
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12304186 |
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PCT/US2007/071551 |
Jun 19, 2007 |
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60815078 |
Jun 20, 2006 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09J
133/04 (20130101); C08J 3/28 (20130101); C09J
133/04 (20130101); C08L 2666/04 (20130101); C08L
2666/04 (20130101); C08L 33/04 (20130101); Y10T
428/2848 (20150115); C08L 2205/02 (20130101) |
Current International
Class: |
C08J
3/28 (20060101); C09J 133/04 (20060101); C08L
33/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2001-164221 |
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Jun 2001 |
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JP |
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2002-372619 |
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Dec 2002 |
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JP |
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WO 2004-111102 |
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Dec 2004 |
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WO |
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Other References
European Search Report from EP Patent No. 07 78 4482, dated Jun.
24, 2010. cited by applicant.
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Primary Examiner: McClendon; Sanza
Attorney, Agent or Firm: Spielbauer; Thomas M. Ehrich; Dena
Dahl; Philip Y.
Claims
What is claimed is:
1. A method of irradiating an article with an electron beam, said
method comprising: providing an electron beam source; providing an
article comprising a layer of a material comprising a blend of (i)
a first acrylic copolymer resulting from polymerization of one or
more monomers A and one or more monomers B, wherein the first
acrylic copolymer has a number average molecular weight, M.sub.n,
ranging from about 150,000 to about 600,000; and (ii) a second
acrylic copolymer resulting from polymerization of one or more
monomers C and one or more monomers D, wherein the second acrylic
copolymer has a number average molecular weight, M.sub.n, ranging
from about 10,000 to about 70,000; wherein monomers B and monomers
D have at least one reactive group that is capable of hydrogen
bonding; the second acrylic copolymer comprises greater than about
10 total parts by weight of the monomers D based a total weight of
the second acrylic copolymer; and the total parts by weight of the
monomers D in the second acrylic copolymer is greater than the
total parts by weight of the monomers B in the first acrylic
copolymer; preparing dose-depth profile calibration curves for the
electron beam source, wherein at least one of the dose-depth
calibration curves exhibits a concave downward dose-depth profile;
selecting a concave downward dose-depth profile of irradiation; and
irradiating the article comprising the layer material at a voltage
and dose according to the selected concave downward dose-depth
profile of irradiation, resulting in an irradiated article; wherein
irradiating according to the selected concave downward dose-depth
profile of irradiation exhibits a minimum of irradiation within a
middle 80% of a thickness of the article.
2. A method of irradiating an article with an electron beam, said
method comprising: providing an electron beam source; providing an
article comprising a layer of a material comprising a blend of (i)
a first acrylic copolymer resulting from polymerization of one or
more monomers A and one or more monomers B, wherein the first
acrylic copolymer has a number average molecular weight, M.sub.n,
ranging from about 150,000 to about 600,000; and (ii) a second
acrylic copolymer resulting from polymerization of one or more
monomers C and one or more monomers D, wherein the second acrylic
copolymer has a number average molecular weight, M.sub.n, ranging
from about 10,000 to about 70,000; wherein monomers B and monomers
D have at least one reactive group that is capable of hydrogen
bonding; the second acrylic copolymer comprises greater than about
10 total parts by weight of the monomers D based a total weight of
the second acrylic copolymer; and the total parts by weight of the
monomers D in the second acrylic copolymer is greater than the
total parts by weight of the monomers B in the first acrylic
copolymer; preparing dose-depth profile calibration curves for the
electron beam source, wherein at least one of the dose-depth
calibration curves exhibits a concave downward dose-depth profile;
selecting a concave downward dose-depth profile of irradiation; and
irradiating the article comprising the layer material at a voltage
and dose according to the selected concave downward dose-depth
profile of irradiation, resulting in an irradiated article; wherein
irradiating according to the selected concave downward dose-depth
profile of irradiation exhibits a minimum of irradiation within a
middle 50% of a thickness of the article.
3. A method of irradiating an article with an electron beam, said
method comprising: providing an electron beam source; providing an
article comprising a layer of a material comprising a blend of (i)
a first acrylic copolymer resulting from polymerization of one or
more monomers A and one or more monomers B, wherein the first
acrylic copolymer has a number average molecular weight, M.sub.n,
ranging from about 150,000 to about 600,000; and (ii) a second
acrylic copolymer resulting from polymerization of one or more
monomers C and one or more monomers D, wherein the second acrylic
copolymer has a number average molecular weight, M.sub.n, ranging
from about 10,000 to about 70,000; wherein monomers B and monomers
D have at least one reactive group that is capable of hydrogen
bonding; the second acrylic copolymer comprises greater than about
10 total parts by weight of the monomers D based a total weight of
the second acrylic copolymer; and the total parts by weight of the
monomers D in the second acrylic copolymer is greater than the
total parts by weight of the monomers B in the first acrylic
copolymer; preparing dose-depth profile calibration curves for the
electron beam source, wherein at least one of the dose-depth
calibration curves exhibits a concave downward dose-depth profile;
selecting a concave downward dose-depth profile of irradiation; and
irradiating the article comprising the layer material at a voltage
and dose according to the selected concave downward dose-depth
profile of irradiation, resulting in an irradiated article; wherein
the irradiated article exhibits a measured stress-relaxation ratio
in a range from about 0.1 to about 0.4.
Description
FIELD
The present disclosure relates to adhesive compositions comprising
a high molecular weight acrylic copolymer and a low molecular
weight acrylic copolymer.
SUMMARY
In one aspect, the present disclosure is directed to adhesive
compositions comprising a blend of a first acrylic copolymer and a
second acrylic copolymer. In one exemplary embodiment, the adhesive
article comprises a blend of a first acrylic copolymer resulting
from polymerization of monomers A and B, wherein (i) the first
acrylic copolymer has a number average molecular weight, M.sub.n,
of at least about 150,000 (or a weight average molecular weight,
M.sub.w, of at least about 450,000), and (ii) monomer B has at
least one reactive group that is capable of hydrogen bonding. The
second acrylic copolymer results from polymerization of monomers C
and D, wherein (i) the second acrylic copolymer has a number
average molecular weight, M.sub.n, of less than about 70,000 (or a
M.sub.w less than about 100,000), (ii) monomer D has at least one
reactive group that is capable of hydrogen bonding, and (iii) the
second acrylic copolymer comprises greater than about 10 parts by
weight (pbw) of monomer D based on a total weight of the second
acrylic copolymer. In some embodiments, the pbw of monomer D in the
second acrylic copolymer is greater than the pbw of monomer B in
the first acrylic copolymer. In some embodiments, the pbw of
monomer D in the second acrylic copolymer is at least about 3 pbw
greater than the pbw of monomer B in the first acrylic
copolymer.
In a further exemplary embodiment of the present disclosure, the
adhesive article comprises a blend of (1) a first acrylic copolymer
formed from monomers A and B, wherein the first acrylic copolymer
(i) has a number average molecular weight, M.sub.n, of at least
about 150,000 (or a M.sub.w of at least about 450,000) and (ii)
comprises less than about 10 percent by weight (pbw) of monomer B
based on a total weight of the first acrylic copolymer, wherein
monomer B has at least one reactive group that is capable of
hydrogen bonding; and (2) a second acrylic copolymer formed from
monomers C and D, wherein the second acrylic copolymer (i) has a
number average molecular weight, M.sub.n, of less than about 70,000
(or a M.sub.w less than about 100,000) and (ii) comprises greater
than about 10 pbw of monomer D based on a total weight of the
second acrylic copolymer.
In yet a further exemplary embodiment of the present disclosure,
the adhesive article comprises an adhesive foam layer comprising a
mixture of a first acrylic copolymer and a second acrylic
copolymer, wherein the first acrylic copolymer (i) is formed from
monomers A and B, wherein monomer B has at least one reactive group
that is capable of hydrogen bonding, (ii) has a number average
molecular weight, M.sub.n, of at least about 150,000 (or a M.sub.w
of at least about 450,000) and (iii) comprises less than about 10.0
percent by weight (pbw) of monomer B based on a total weight of the
first acrylic copolymer; and the second acrylic copolymer (i) is
formed from monomers B and C, (ii) has a number average molecular
weight, M.sub.n, of less than about 70,000 (or a M.sub.w of less
than about 100,000) and (iii) comprises a percent by weight (pbw)
of monomer B based on a total weight of the second acrylic
copolymer, wherein the pbw of monomer B of the second acrylic
copolymer is greater than the pbw of monomer B of the first acrylic
copolymer.
In another aspect, the present disclosure provides adhesive
articles comprising one or more adhesive core layers and,
optionally, one or more additional layers. In one exemplary
embodiment of the present disclosure, the adhesive article
comprises (a) an adhesive core layer comprising the above-described
blend or mixture of a first acrylic copolymer having a relatively
high molecular weight and a second acrylic copolymer having a
relatively low molecular weight; and (b) at least one additional
layer on a major surface of the adhesive core layer. The adhesive
article of the present disclosure may further comprise other layers
including, but not limited to, a second adhesive layer, such as a
pressure-sensitive adhesive layer and/or a heat-activatable
adhesive layer, at least one release liner, at least one
non-adhesive substrate layer, or any combination thereof.
In another aspect, the present disclosure is further directed to
methods of making adhesive articles. In one exemplary embodiment,
the method of making an adhesive article comprises the steps of
extruding a blend of (1) a first acrylic copolymer formed from
monomers A and B, wherein the first acrylic copolymer (i) has a
number average molecular weight, M.sub.n, of at least about 150,000
(or a M.sub.w of at least about 450,000) and (ii) comprises less
than about 10 percent by weight (pbw) of monomer B based on a total
weight of the first acrylic copolymer, wherein monomer B has at
least one reactive group that is capable of hydrogen bonding; and
(2) a second acrylic copolymer formed from monomers C and D,
wherein the second acrylic copolymer (i) has a number average
molecular weight, M.sub.n, of less than about 70,000 (or a M.sub.w
of less than about 100,000) and (ii) comprises greater than about
10 pbw of monomer D based on a total weight of the second acrylic
copolymer; and exposing the extrudate to an amount of irradiation
so as to obtain a controlled degree of crosslinking between the
first acrylic copolymer and the second acrylic copolymer.
Desirably, the controlled degree of crosslinking between the first
acrylic copolymer and the second acrylic copolymer results in a
crosslinked adhesive article having a stress relaxation ratio
G(300)/G(0.1) as measured by a Stress Relaxation Test at 70.degree.
C. of less than or equal to about 0.30, desirably, from about 0.13
to about 0.30.
In another exemplary embodiment, the method of making an adhesive
article comprises providing an electron beam generating apparatus
having a first control for an accelerating voltage and a second
control for a dose; providing a material to be cured having a
composition, a thickness, and a density; determining one or more
desired properties capable of resulting from a controlled amount of
crosslinking using the electron beam generating apparatus; and
using a Minimum Calculated Core Cure value of the material based on
dose-depth profile calibration curves for the electron beam
generating apparatus and for the material to be cured, crosslinking
the material at a voltage and dose that results in the one or more
desired properties. The exemplary method may further comprise
preparing the dose-depth profile calibration curves for the
electron beam generating apparatus and for the material to be cured
based on the composition, thickness, and density of the material;
and determining the Minimum Calculated Core Cure value based on the
dose-depth profile calibration curves.
These and other features and advantages of the present disclosure
will become apparent after a review of the following detailed
description of the disclosed embodiments and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of an exemplary adhesive article
according to some embodiments of the present disclosure;
FIG. 2 is a cross-sectional view of an exemplary tape according to
some embodiments of the present disclosure in roll form comprising
an exemplary adhesive article having a removable release liner on
an outer surface thereon;
FIG. 3 is a schematic drawing of an exemplary extrusion process for
preparing adhesive articles according to some embodiments of the
present disclosure;
FIG. 4 provides an exemplary graph showing electron beam radiation
dose versus tape depth for the sample tape of Example 1 after
electron beam radiation exposure to one outer surface;
FIG. 5 provides an exemplary graph showing electron beam radiation
dose versus tape depth for the sample tape of Example 1 after
electron beam radiation exposure to both outer surfaces;
FIG. 6 provides an exemplary graph showing electron beam radiation
dose versus tape depth for the sample tape of Example 1 after
electron beam radiation exposure to both outer surfaces at a lower
accelerating voltage than used in the trial shown in FIG. 5;
FIG. 7 provides an exemplary graph showing Stress Relaxation at
70.degree. C. versus Minimum Calculated Core Cure for sample tapes
of Examples 1-8; and
FIG. 8 provides an exemplary graph showing Stress Relaxation at
70.degree. C. versus the product of the Average Calculated Core
Cure (ACCC) and the Minimum Calculated Core Cure (MCCC) for sample
tapes of Examples 1-8.
DETAILED DESCRIPTION
Generally, the adhesive compositions of the present disclosure
comprise a mixture of a high molecular weight acrylic copolymer and
a low molecular weight acrylic copolymer. In some embodiments, the
adhesive compositions may optionally further comprise one or more
additional components as described below.
The high molecular weight acrylic copolymer is also referred to
herein as the "first acrylic copolymer." The first acrylic
copolymer is formed from monomer(s) A and monomer(s) B. As used
herein, the term "monomer(s)" indicates that one or more monomers
may be selected. For example, "monomer(s) A" may include one or
more monomers selected from those monomers suitable for use as a
monomer A. Similarly, "monomer(s) B" refers to the one or more
monomers selected from those monomers suitable for use as a monomer
B.
Suitable monomers for monomer A include, but are not limited to,
acrylic or methacrylic esters of non-tertiary alkyl alcohols, with
the alkyl groups having from 1 to 20 carbon atoms (for example,
from 3 to 18 carbon atoms). Such monomers A include, but are not
limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl
(meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate,
cyclohexyl (meth)acrylate, isooctyl (meth)acrylate, octadecyl
(meth)acrylate, tridecyl (meth)acrylate, nonyl (meth)acrylate,
decyl (meth)acrylate, dodecyl (meth)acrylate, isobornyl
(meth)acrylate, 2-phenoxyethyl (meth)acrylate, benzyl
(meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate,
phenyl (meth)acrylate, or any combination thereof. As used herein,
the term "(meth)acrylate" is used to refer to either one or both of
the acrylate and methacrylate species. For example, methyl
(meth)acrylate refers to methyl acrylate, methyl methacrylate, and
combinations thereof.
Suitable monomers for monomer B include, but are not limited to,
acrylic, methacrylic, or other unsaturated acids with the alkyl
group having from 1 to 20 carbon atoms (for example, from 3 to 18
carbon atoms). Such monomers B include, but are not limited to,
acrylic acid, methacrylic acid, itaconic acid, citraconic acid,
maleic acid, fumaric, acid, and itaconic, citraconic, maleic and
fumaric monoesters (these are diacid compounds and their monoester
offer an acid group), or any combination thereof. Other suitable
monomers B include acrylonitrile, methacrylonitrile, vinyl acetate,
N-vinyl pyrrolidone, isobornyl acrylate, cyano ethyl acrylate,
N-vinylcaprolactam, maleic anhydride, hydroxyalkylacrylates,
N,N-dimethyl aminoethyl (meth)acrylate, N,N-diethylacrylamide,
vinylidene chloride, styrene, vinyl toluene, hydroxyarylacryaltes,
tetrahydrofurfuryl(meth)acrylate, and alkyl vinyl ethers.
In some embodiments, at least one monomer B comprises a monomer
having at least one reactive group thereon that is capable of
hydrogen bonding (for example, --COOH).
In some embodiments, the first acrylic copolymer comprises less
than about 10 percent by weight (pbw) of monomer(s) B based on a
total weight of the first acrylic copolymer. In some embodiments,
the first acrylic copolymer comprises from about 2 to about 7 pbw
of monomer(s) B based on a total weight of the first acrylic
copolymer.
The high molecular weight acrylic copolymer component (or first
acrylic copolymer) may be formed using conventional polymerization
techniques. These techniques are generally known in the industry
and include processes such as thermally initiated polymerization,
photoinitiation, suspension polymerization, and the like.
Typically, in addition to monomer(s) A and monomer(s) B, an
appropriate polymerization initiator can be used to initiate
polymerization of monomers A and B. Suitable initiators for
photoinitiation include, but are not limited to,
2,2-dimethoxy-2-phenylacetophenone (for example, IRGACURE.TM. 651
commercially available from Ciba-Geigy (Hawthorne, N.Y.));
2-hydroxy-1-(4-*2-hydroxyethoxy)phenyl)-2-methyl-1propanone (for
example, DAROCURE.TM. 2959 commercially available from Ciba-Geigy);
2-hydroxy-2-methyl-1-phenyl-1-propanone (for example, DAROCURE.TM.
1173 commercially available from Ciba-Geigy); diphenyl
(2,4,6-trimethylbenzoyl)-phosphine oxide (for example, LUCIRIN.TM.
TPO commercially available from BASF Corporation (Florham Park,
N.J.)); 1-hydroxycyclohexyl phenyl ketone (for example,
IRGACURE.TM. 184 commercially available from Ciba-Geigy);
2-methyl-1-(4-(methylhio)phenyl)-2-(4-morpholinyl)-1-propanone (for
example, IRGACURE.TM. 907 commercially available from Ciba-Geigy);
2-benzyl-2-(dimethylamino)-1-(4-(4-morpholinyl)phenyl)-1-butanone
(for example, IRGACURE.TM. 369 commercially available from
Ciba-Geigy); phenylbis (2,4,6-trimethyl benzoyl)-phosphine oxide
(for example, IRGACURE.TM. 819 commercially available from
Ciba-Geigy), or ethyl 2,4,6-trimethylbenzoylphenylphosphinate (for
example, LUCIRIN.TM. TPO-L commercially available from BASF
Corporation).
Further, a chain transfer agent may be present during the
polymerization reaction. Chain transfer agents may be used to
control the molecular weight of the resulting polymer and reduce
the amount of residual monomer remaining after the polymerization
reaction. Suitable chain transfer agents include, but are not
limited to, isooctyl thioglycolate (IOTG) (for example, IOTG
commercially available from Daicel Chemical Industries, LTD (Tokyo,
JAPAN) or from Dow Chemical Company (Midland, Mich.)); n-octyl
mercaptan (for example, commercially available from Arkema
(Philadelphia, Pa.); n-decyl mercaptan (for example, commercially
available from Philips Petroleum (Houston, Tex.)); n-hexyl
mercaptan (for example, commercially available from Arkema);
n-octadecyl mercaptan (for example, commercially available from
ACIMA Chemical Industries (Philadelphia, Pa.)); n-dodecyl mercaptan
(for example, commercially available from Arkema); tert-dodecyl
mercaptan (for example, commercially available from Arkema); and
2-ethylhexyl thioglycolate (for example, commercially available
from Arkema).
In some embodiments, the first acrylic copolymer has a number
average molecular weight, M.sub.n, of at least about 150,000. In
some embodiments, the first acrylic copolymer has a weight average
molecular weight, M.sub.w of at least about 450,000. As used
herein, number average molecular weight, M.sub.n, and weight
average molecular weight, M.sub.w, are measured using the Gel
Permation Chromatography (GPC) test method described in the "Test
Methods" section below.
In some embodiments, the first acrylic copolymer has a M.sub.n
ranging from about 150,000 to about 600,000 (and/or a M.sub.w of at
least about 450,000 to about 2,000,000). In some embodiments, the
first acrylic copolymer has a M.sub.n ranging from about 160,000 to
about 350,000 (and/or a M.sub.w of at least about 480,000 to about
1,000,000) and in some embodiments, a M.sub.n from about 170,000 to
about 300,000 (and/or a M.sub.w of at least about 500,000 to about
900,000).
Generally, the first acrylic copolymer may be present in an amount
that varies depending on the desired properties of the resulting
adhesive composition. Typically, the first acrylic copolymer is
present in an amount greater than about 50 percent by weight (pbw)
based on a total weight of the adhesive composition. In some
embodiments, the first acrylic copolymer is present in an amount
greater than about 60, greater than about 65, or even greater than
about 70 pbw. In some embodiments, the first acrylic copolymer is
present in an amount ranging from about 75 to about 98 pbw, based
on a total weight of the adhesive composition.
Adhesive compositions according to the present disclosure further
comprise a low molecular weight acrylic copolymer, also referred to
herein the "second acrylic copolymer." The second acrylic copolymer
is formed from monomer(s) C and monomer(s) D. Suitable monomers for
monomer C are the same as those suitable for monomer A, and are
described above with respect to the first acrylic copolymer.
Similarly, suitable monomers for monomer D are the same as those
suitable for monomer B, as described above with respect to the
first acrylic copolymer.
Generally, each of the monomer(s) A, B, C, and D are independently
selected. In some embodiments, one or more of the monomers selected
for use as monomer(s) A may also be selected for use as monomer(s)
C. Similarly, in some embodiments, one or more monomers selected
for use as monomer(s) B may also be selected for use as monomer(s)
D.
In some embodiments, the second acrylic copolymer comprises greater
than about 10 pbw of monomer(s) D based on a total weight of the
second acrylic copolymer. In some embodiments, the second acrylic
copolymer comprises from about 12 to about 30 pbw of monomer(s) D,
and, in some embodiments, from about 15 to about 20 pbw of
monomer(s) D, based on a total weight of the second acrylic
copolymer.
Typically, the pbw of monomer(s) D of the second acrylic copolymer
is greater than the pbw of monomer(s) B of the first acrylic
copolymer. In some embodiments, the pbw of monomer(s) D of the
second acrylic copolymer is at least 3 pbw greater than the pbw of
monomer(s) B of the first acrylic copolymer. In other embodiments,
the pbw of monomer(s) D of the second acrylic copolymer is at least
5 pbw (or at least 8 pbw, or at least 10 pbw, or at least 12 pbw,
or at least 15 pbw) greater than the pbw of monomer(s) B of the
first acrylic copolymer.
In some embodiments, at least one monomer C of the second acrylic
copolymer is identical to at least one monomer A of the first
acrylic copolymer. In some embodiments, all of the monomer(s) C of
the second acrylic copolymer are the same as the monomer(s) A of
the first acrylic copolymer. In other embodiments, each monomer C
of the second acrylic copolymer differs from all of the monomer(s)
A of the first acrylic copolymer.
In some embodiments, the second acrylic copolymer is substantially
free of "photoinitiator monomers," that is, (i) monomers containing
reactive groups that are susceptible to forming radicals in the
presence of a photoinitiator and (ii) monomers, which are
themselves photoactive radical formers. In such an exemplary
embodiment, the second acrylic copolymer is formed from monomers C
and D, and possibly additional monomers, as long as the additional
monomers are not photoinitiator monomers. In some embodiments, the
first acrylic copolymer is also substantially free of
photoinitiator monomers.
The low molecular weight acrylic copolymer component (that is, the
second acrylic copolymer) may be formed using conventional
polymerization techniques as discussed above with regard to the
high molecular weight acrylic copolymer component (or first acrylic
copolymer). In addition to monomer(s) C and monomer(s) D, a
polymerization initiator and/or chain transfer agent may be present
during the polymerization reaction.
In some embodiments, the second acrylic copolymer has a number
average molecular weight, M.sub.n, of less than about 70,000. In
some embodiments, the second acrylic copolymer has weight average
molecular weight, M.sub.w, of less than about 100,000. In some
embodiments, the second acrylic copolymer has a number average
molecular weight, M.sub.n, ranging from about 10,000 to about
70,000 (and/or a M.sub.w of from about 14,000 to about 100,000). In
some embodiments, the second acrylic copolymer has a number average
molecular weight, M.sub.n, ranging from about 15,000 to about
60,000 and/(or a M.sub.n of from about 20,000 to about 84,000),
and, in some embodiments, a M.sub.n of from about 20,000 to about
55,000 (and/or a M.sub.w of from about 28,000 to about 77,000).
The second acrylic copolymer may be present in an amount that
varies depending on the desired properties of the resulting
adhesive composition. Typically, the second acrylic copolymer is
present in an amount less than about 50 pbw based on a total weight
of the adhesive composition. In some embodiments, the second
acrylic copolymer is present in an about less than about 40 pbw, or
less than about 35 pbw, or even less than about 30 pbw. In some
embodiments, the second acrylic copolymer is present in an amount
ranging from about 25 to about 2 pbw, based on a total weight of
the adhesive composition.
In some embodiments, various additives or other ingredients may be
added to the adhesive composition to impart or modify particular
characteristics of the ultimate adhesive composition. The additives
may be present in any amount as long as the amount does not
adversely interfere with the desired properties of the adhesive
composition. In some embodiments, the adhesive composition
comprises one or more additives in an amount of up to about 50
weight percent, based on the total weight of the adhesive
composition. Exemplary additives include, but are not limited to,
tackifiers, plasticizers, fillers, antioxidants, pigments,
diffusing materials, fibers, filaments, silicas, treated silicas,
carbon black, dyes, expandable polymeric microspheres,
non-expandable polymeric or glass microspheres, chain transfer
agents, chemical blowing agents, reinforcing agents, calcium
carbonate, toughening agents, fire retardants, acrylate-insoluble
polymers, finely ground polymeric particles such as polyester,
nylon, or polypropylene, stabilizers, and combinations thereof.
In one exemplary embodiment, the adhesive composition comprises a
foam having voids throughout at least a portion of the adhesive
composition. Voids may be formed by incorporating a variety of
additives into the adhesive core layer prior to or during formation
of the adhesive core layer. For example, expandable polymeric
microspheres, hollow polymeric or glass microspheres, foaming
agents, or any combination thereof may be incorporated into the
adhesive core layer in order to form voids throughout at least a
portion of the adhesive core layer. Suitable void-forming materials
include, but are not limited to, void-forming materials disclosed
in U.S. Pat. No. 6,103,152. In some embodiments, expandable
polymeric microspheres, such as those disclosed in U.S. Pat. No.
6,103,152, are incorporated into the adhesive composition in an
amount ranging from about 1 pbw to about 15 pbw, and, in some
embodiments, from about 2 pbw to about 6 pbw, based on a total
weight of the adhesive composition.
In some embodiments, the adhesive composition may be an outermost
layer of the adhesive article. In some embodiments, the adhesive
composition may be sandwiched between two or more similar or
dissimilar substrates.
In some embodiments, the adhesive articles of the present
disclosure comprise one or more layers with at least one layer, for
example, a core layer, being formed from an adhesive composition
comprising a crosslinkable or crosslinked mixture of high and low
molecular weight acrylic copolymers. As shown in FIG. 1, exemplary
adhesive article 40 comprises adhesive core layer 41 having first
major surface 42 and second major surface 44. In some embodiments,
adhesive article 40 includes at least one of first additional layer
43 on first major surface 42, and second additional layer 45 on
second major surface 44. Exemplary adhesive article 40 further
comprises first outer major surface 46 on first additional layer 43
and second outer major surface 48 on second additional layer
45.
Generally, the adhesive core layer comprises an intimate mixture
(or blend) of the above-described first and second acrylic
copolymers. In some embodiments, the first and second acrylic
copolymers are mixed with one another so as to result in a desired
degree of hydrogen bonding between the first and second acrylic
copolymers. In some embodiments, the first and second acrylic
copolymers are mixed so as to result in a degree of hydrogen
bonding that provides an adhesive core having a desired amount of
stress relaxation, while maintaining desired performance during
high temperature shear.
In some embodiments, the first and second acrylic copolymers are
substantially miscible with one another so that the resulting
mixture comprises a single phase or domain. In other embodiments,
the first and second acrylic copolymers, when mixed, form two
separate phases or domains intimately blended with one another. In
either case, the resulting mixture provides a degree of hydrogen
bonding between the first and second acrylic copolymers.
In one exemplary embodiment in which the first and second acrylic
copolymers are extruded with one another, the polymers may be
immiscible with one another so that small domains of each polymer
are present in the extrudable mixture. By minimizing the time
between mixing and extruding or by using in-line static mixing,
extrusion of the adhesive mixture can occur before any substantial
amount of phase separation takes place. By cooling the extrudate in
a relatively rapid manner, the first and second acrylic copolymers
remain in an intimate mixture, which can then be subsequently
crosslinked as described below.
In some embodiments, the adhesive composition possesses a stress
relaxation ratio (G(300)/G(0.1)) value (that is, "SRR value") of
less than about 0.3, and in some embodiments, from about 0.1 to
about 0.3, as measured by the "Stress Relaxation Test" conducted at
70.degree. C. (as described below in the "Test Methods" section).
The SSR value of a given adhesive composition provides an
indication of the ability of the adhesive to (i) deform under
continuous load and (ii) resist deformation as the adhesive extends
under the continuous load. FIG. 7 provides an exemplary graph
showing the change in SRR values of various polymer compositions as
the amount of exposure to electron beam radiation increases. The
controlled amount of exposure to electron beam radiation is
measured as a minimum calculated core cure ("MCCC") amount as
described in the "Test Methods" section below.
The calculated cure is dependent on the specific equipment used to
deliver the electron beam, and those skilled in the art can define
a dose calibration model for the equipment used. For example, in
the present disclosure, the radiation processing is performed on an
Energy Sciences, Inc. (Wilmington, Mass.), Model CB-300 electron
beam generating apparatus equipped with a 76.2 micrometer (.mu.m)
(0.003 inch) thick, 30.48 millimeter (mm) (12 inch) wide polyester
terephthalate support film running through an inert chamber as
described below.
In one exemplary embodiment, adhesive compositions may have a SSR
value of less than about 0.35, and in some embodiments, from about
0.1 to about 0.3, after exposure to electron beam radiation. In a
further exemplary embodiment, the adhesive composition has a SSR
value of less than about 0.28, for example, from about 0.12 to
about 0.25, or even from about 0.15 to about 0.23, after exposure
to electron beam radiation.
As discussed above, in some embodiments, the adhesive composition
comprises a foam core layer. Solid adhesive core layers (that is,
non-foam layers) typically have a layer density ranging from about
0.92 g/cc to about 1.2 g/cc, while adhesive foam core layers,
themselves, typically have a layer density ranging from about 0.3
g/cc to about 0.7 g/cc. Typically, articles resulting from the
combination of one or more skin layers with the adhesive core
layers have an overall density ranging from about 0.4 grams per
cubic centimeter (g/cc) to about 0.8 g/cc.
In some embodiments, the adhesive composition exhibits resistance
to a static shear load, which is measured by a hanging shear test
(described in the "Test Methods" section below). Hanging shear
measures the ability of a defined area of a pressure sensitive
adhesive (PSA) adhesive bonded between two rigid surfaces to hold a
fixed weight hanging from one edge of one of the surfaces without
substantially sliding apart (falling off). It is usually measured
in minutes of hang time with a given area, (typically about either
323 sq mm or 635 sq mm) and a given load (typically 500 g/323 sq mm
or 1000 g/625 sq mm at 70.degree. C. or 2 kg/625 sq mm. at room
temperature).
In some embodiments, the adhesive composition of the present
disclosure remain intact after 5,000 minutes, and, in some
embodiments, after 10,000 minutes with a 500 gram weight hanging
from one panel both at 70.degree. C. and at room temperature. The
70.degree. C. temperature objective is typically more difficult to
meet.
In addition to the adhesive core layer described above, in some
embodiments, the present disclosure provides adhesive articles that
may include one or more additional layers on either side of the
adhesive core layer. The one or more additional layers may each
independently be temporarily or permanently attached to an outer
surface of the adhesive core layer. Suitable additional layers are
described below.
Referring to exemplary adhesive article 40 shown in FIG. 1, first
additional layer 43 and/or second additional layer 45 could be
adhesive layers. The one or more additional adhesive layers may be
any suitable adhesive known in the art, including, for example, an
adhesive that is activatable by pressure, heat or a combination
thereof. Suitable adhesives include, but are not limited to,
adhesive compositions comprising (meth)acrylate copolymers,
rubber/resins, epoxies, urethanes or combinations thereof. Each
additional adhesive layer may be applied to an outer surface of the
adhesive core layer by any known method including, for example, by
solution, water-based or hot-melt coating methods, including hot
melt co-extrusion methods where one or more layers are formed
simultaneously with the above-described adhesive core layer. Each
additional adhesive layer may include hot melt coated formulations,
transfer-coated formulations, solvent-coated formulations, and
latex-coated formulations, as well as, laminating,
thermally-activated, and water-activated adhesives and bonding
agents. In some embodiments, at least one of the additional
adhesive layers, when present, comprises a pressure sensitive
adhesive (PSA), a heat-activatable adhesive layer (for example, a
hot melt adhesive layer), or a combination thereof.
Examples of suitable pressure sensitive adhesives include, but are
not limited to, PSAs based on general compositions of
poly(meth)acrylate; polyvinyl ether; diene rubber such as natural
rubber, polyisoprene, and polybutadiene; polyisobutylene;
polychloroprene; butyl rubber; butadiene-acrylonitrile polymer;
thermoplastic elastomer; block copolymers such as styrene-isoprene
and styrene-isoprene-styrene (SIS) block copolymers,
ethylene-propylene-diene polymers, and styrene-butadiene polymers;
poly-alpha-olefin; amorphous polyolefin; silicone;
ethylene-containing copolymer such as ethylene vinyl acetate,
ethylacrylate, and ethyl methacrylate; polyurethane; polyamide;
epoxy; polyvinylpyrrolidone and vinylpyrrolidone copolymers;
polyesters; and mixtures or blends (continuous or discontinuous
phases) of the above.
Examples of suitable heat-activatable adhesives include, but are
not limited to, heat-activatable adhesives based on general
compositions of polyolefins, copolymers containing olefin monomers,
etc.
As discussed with regard to the adhesive core layer above, each
additional adhesive layer adhesive composition may contain
additives.
In some embodiments, the adhesive article comprises an adhesive
core layer in combination with at least one additional adhesive
layer, wherein the at least one additional adhesive layer is
present on a major surface of the adhesive core layer in the form
of a PSA layer. In a further exemplary embodiment, the adhesive
article comprises an adhesive core layer in combination with PSA
layers on both major surfaces of the adhesive core layer. In either
of these embodiments, the PSA may comprise a PSA containing a
styrene-isoprene asymmetric star block copolymer such as disclosed
in U.S. Pat. No. 5,393,787 issued to Nestegard et al., U.S. Pat.
No. 6,503,621 issued to Ma et al., or U.S. Pat. No. 6,630,531,
issued to Khandpur et al., all of which are assigned to 3M
Innovative Properties Company (St. Paul, Minn.), the subject matter
of which is hereby incorporated herein in its entirety.
In addition to the adhesive core layer and any optional additional
adhesive layers described above, the adhesive articles may include
one or more release liners to protect an outer surface of an
adhesive core layer or any additional adhesive layer of the
adhesive article.
As shown in FIG. 2, exemplary adhesive article 50 comprises
adhesive core layer 51 having first major surface 52 and second
major surface 54, release liner 53 on first major surface 52, and
an additional layer 55 on second major surface 54. Exemplary
adhesive article 50 further comprises first outer major surface 56
on additional layer 55, and release liner inner surface 58 and
release liner outer surface 60 on release liner 53.
Release liners are well-known in the art, and any known release
liner may be used. Typically, the release liner comprises a film or
paper substrate coated with a release material. Commercially
available release liners include, but are not limited to, silicone
coated papers, and silicone coated films, such as polyester films.
Examples of suitable release liners include, but are not limited
to, release liners sold under the trade designation AKROSIL.TM.
available from Akrosil Europe (Huerlen, Netherlands) and
International Paper (Menasha, Wis.); and release liners available
from Daubert Coated Products, Inc. (Dixon, Ill.). In some
embodiments, the release liner comprises AKROSIL.TM. Paper Liner
ZG-3223 (Akrosil Europe, Huerlen, Netherlands) or AKROSIL.TM. Paper
Liner SBL 60 SC SILOX F1U/F4B (International Paper, Menasha,
Wis.).
In one exemplary embodiment, the above-described adhesive article
comprises a release liner as disclosed in U.S. Pat. Nos. 6,835,422;
6,805,933; 6,780,484; or 6,204,350 assigned to 3M Innovative
Properties Company.
Referring again to FIG. 2, it should be noted that release liner 53
may provide release properties along release liner inner surface
58, release liner outer surface 60, or both. For example, if
additional layer 55 is an additional adhesive layer, such as a PSA,
release liner outer surface 60 of release liner 53 will desirably
have release properties. If first outer major surface 56 on
additional layer 55 does not have any degree of adhesive tackiness,
release liner outer surface 60 of release liner 53 does not need
release properties.
In a further embodiment, additional layer 55 on second major
surface 54 of adhesive core layer 51 also comprises a release liner
such that release liner 53 and additional layer 55 protect
protection to first major surface 52 and second major surface 54 of
adhesive core layer 51.
In some embodiments, adhesive articles of the present disclosure
may also include one or more additional layers that may provide
additional temporary or permanent properties to the adhesive
articles. Suitable additional layers may be positioned on one or
both sides of the adhesive core layer. In some embodiments, the one
or more additional layers are flexible such that the resulting
adhesive article may be rolled into a roll. The one or more
additional layers may function as, for example, tie layers, primer
layers, or barrier layers. Suitable additional layers include, but
are not limited to, polymer films, metal foils, papers, foam
sheets, and fabrics. The one or more additional layers may be
attached to the adhesive core layer by a pressure-sensitive
adhesive as described above or by the adhesive core layer
composition itself.
Examples of suitable substrates include, but are not limited to,
glass, metal, plastic, wood, and ceramic substrates, painted
surfaces of these substrates, and the like. Representative plastic
substrates include polyester, polyvinyl chloride,
ethylene-propylene-diene monomer rubber, polyurethanes, polymethyl
methacrylate, engineering thermoplastics (for example,
polyphenylene oxide, polyetheretherketone, polycarbonate), and
thermoplastic elastomers. The substrate may also be a woven or
knitted fabric formed from threads of synthetic or natural
materials such as, for example, cotton, nylon, polyamide, rayon,
glass, carbon or ceramic material. The substrate may also be made
of a nonwoven fabric such as air-laid webs of natural or synthetic
fibers or blends thereof.
The present disclosure also provides methods of making adhesive
compositions and articles. In one exemplary embodiment, the method
of making an adhesive composition comprises mixing the
above-described adhesive composition components. Desirably, the
components are mixed to form a substantially homogeneous adhesive
composition mixture. The method may further comprise a number of
optional steps depending on the ultimate use of the adhesive
composition. For example, the method may comprise a method of
forming an adhesive article, wherein the method comprises shaping
the adhesive composition into an adhesive article (for example, a
coating step or an extrusion step). In addition, post-shaping steps
may be used to impart desired physical properties to the shaped
adhesive article. For example, the method of forming an adhesive
article may further comprise exposing a portion of the shaped
adhesive article to radiation in order to crosslink one or more
components within the shaped adhesive article.
Exemplary methods of making adhesive compositions and adhesive
articles are described below.
Adhesive core layers may be prepared using conventional method
steps such as those disclosed in U.S. Pat. No. 6,103,152 issued to
Gehlsen. Typically, the method of making an adhesive article
comprising at least one adhesive core layer comprises melt-mixing
the above-described adhesive components to form a substantially
homogeneous mixture, shaping the substantially homogeneous mixture
to form a shaped adhesive article, and allowing the shaped adhesive
article to cool. In some embodiments, the shaping step may comprise
providing the adhesive composition mixture onto a temporary
substrate (for example, a release liner) or permanent substrate
(for example, a backing layer or other adhesive layer), for
example, by a coating step. In other embodiments, the shaping step
may comprise providing the adhesive composition mixture onto a
temporary substrate (for example, a release liner) or permanent
substrate (for example, a backing layer or other adhesive layer)
via an extrusion step.
In one embodiment, the method of forming an adhesive article
comprises an extrusion step. FIG. 3 depicts an extrusion apparatus
suitable for use in some methods of the present disclosure. In this
exemplary embodiment, each of the above-described copolymers (for
example, first and second acrylic copolymers) may be initially fed
into a first heating and conveying device 10 such as a roll feeder,
single screw extruder (as shown), grid melter, or bonnot, where
input materials, such as each of the copolymers are melted. The
copolymers may be added to heating and conveying device 10 in any
convenient form, including pellets, billets, packages, strands, and
ropes. At the end the heating and conveying device, is typically, a
metering device (not shown), such as a gear melt pump, where the
output rate of the melted polymer can be controlled. At the end of
the metering pump, a heated hose (not shown) may be used to convey
the metered output to, for example, a twin screw extruder 12. Twin
screw extruder 12 is typically fitted with ports (not shown) along
its length, for inputting metered liquids, such as melted
copolymers, tackifiers, stabilizers, and the like, usually under
pressure. Twin screw extruder 12 also has open ports 13 that are
not under pressure, where dry solids, such as stabilizers,
pigments, rubbers and/or plastic pellets, expandable microspheres,
and the like can be supplied. The dry solid materials are typically
conveyed to open port 13 via a weight loss feeder (not shown) to
control the feed rate. Along the length of the twin screw extruder
12 are mixing kneaders and/or conveying sections, which allow
control of the degree of mixing of the separately fed materials.
Various sections of the twin screw extruder 12 can be heated or
cooled to control the temperature of the mixing and conveying
process, as well as the twin screw turning rate.
Desirably, mixing is carried out at a temperature insufficient to
cause substantial microsphere expansion within the twin screw
extruder 12 for embodiments in which expandable microspheres are
present during mixing. For example, mixing temperatures may be from
about 100.degree. C. to about 125.degree. C. In other embodiments,
it is also possible to use temperatures in excess of a microsphere
expansion temperature (for example, mixing temperatures may be from
about 125.degree. C. to about 160.degree. C.) either because the
pressures of the extruder/mixing/conveying process prevent
substantial expansion until the mixture reaches the coating head or
because the temperature can be reduced prior to adding the
microspheres. In actual practice, some of the expandable
microspheres can be broken during mixing, and such conditions may
be optimized to minimize breakage. Specific temperatures,
pressures, shear rates, and mixing times are selected based upon
the particular composition being processed.
At the end of the extruder is, typically, a gear melt pump 16,
which provides an output stream free of pressure surges. The
metered output is typically fed via a heated pipe or hose 18 to a
coating head, such as a die 14 (for example, a contact or drop
die). Optionally, an in-line mixing device (not shown), such as a
static mixer, may be used to optimize the mixture and temperature
homogeneity, especially if the heated pipe or hose 18 is long. The
temperature and pressure within die 14 is desirably controlled to
cause expansion of expandable microspheres (when present) within
the die lips, as the composition exits the coating head 14 and
experiences the pressure drop to normal atmospheric conditions.
The shape of the adhesive core layer is dictated by the shape of
die 14. Although a variety of shapes may be produced, the adhesive
core layer is typically produced in the form of a continuous or
discontinuous sheet having outer major surfaces separated from one
another by a peripheral edge.
As shown in FIG. 3, the adhesive core layer 23 may optionally be
combined with a temporary or permanent layer 20 (for example, a
release liner) dispensed from a feed roll 22. Suitable temporary
layers for layer 20 include, but are not limited to, silicone
release liners, polyester films (for example, polyethylene
terephthalate films), and polyolefin films (for example,
polyethylene films), as well as other release layers described
above. Layer 20 and the adhesive core layer are then laminated
together between a pair of nip rollers 24. Following lamination,
the adhesive core layer is optionally exposed to radiation from an
electron beam source 26 to crosslink the adhesive core layer. The
electron beam can be provided from one or both sides of the core
layer either through a temporary or permanent layer, or directly
onto an exposed surface of the core layer. Other sources of
radiation (for example, ion beam, gamma radiation, and ultraviolet
radiation) may be used as well. Crosslinking improves the cohesive
strength of the adhesive core layer. Following exposure, the
laminate is rolled up to form a take-up roll 28.
In some embodiments, the method of forming an adhesive article
comprises exposing the adhesive core layer to electron beam
radiation so as to provide a controlled amount of crosslinking
between the first and second acrylic copolymers of the adhesive
core layer. Depending on the thickness and density of the adhesive
composition, a particular accelerating voltage and dose of the
electron beam is directed at the adhesive mass from one or both
sides of the sheet so that the resulting adhesive core layer has a
desired balance of properties, for example, shear strength, stress
relaxation, and the like.
In some embodiments, the method of forming an adhesive article
comprises extruding a blend of the first acrylic copolymer and the
second acrylic copolymer; and exposing the extrudate to an amount
of irradiation so as to obtain a controlled degree of crosslinking
between the first acrylic copolymer and the second acrylic
copolymer. In some embodiments, the resulting adhesive article has
a stress ratio G(300)/G(0.1) as measured by a Stress Relaxation
Test at 70.degree. C. of less than about 0.30, and, in some
embodiments, from about 0.10 to about 0.30 as discussed above.
Further, as discussed above, the relative amounts (that is, pbw) of
monomer(s) B and D in the first and second acrylic copolymers,
respectively, may be varied so as to provide a desired degree of
hydrogen bonding between the first and second acrylic copolymers.
As discussed above, in some embodiments, the pbw of monomer(s) D in
the second acrylic copolymer is greater than the pbw of monomer(s)
B in the first acrylic copolymer, and, in some embodiments, at
least about 3 pbw greater than the pbw of monomer B in the first
acrylic copolymer.
In some embodiments, the method of making an adhesive article
comprises providing an electron beam generating apparatus having a
first control for an accelerating voltage and a second control for
a dose; providing a material to be cured having a composition, a
thickness, and a density; determining one or more desired
properties capable of resulting from a controlled amount of
crosslinking using the electron beam generating apparatus; and
using a Minimum Calculated Core Cure value of the material based on
dose-depth profile calibration curves for the electron beam
generating apparatus and for the material to be cured, crosslinking
the material at a voltage and dose that results in the one or more
desired properties. For example, the one or more desired properties
may comprise stress relaxation, shear strength, or a combination
thereof. This exemplary method may further comprise preparing the
dose-depth profile calibration curves for the electron beam
generating apparatus and for the material to be cured based on the
composition, thickness, and density of the material; and
determining the Minimum Calculated Core Cure value based on the
dose-depth profile calibration curves. As described in the Examples
below, a Monte Carlo code can be used to assist in the
determination of the Minimum Calculate Core Cure value.
The exemplary method of making an adhesive article using a Minimum
Calculated Core Cure value of the material based on dose-depth
profile calibration curves for the electron beam generating
apparatus and for the material to be cured desirably utilizes a
cure procedure that results in a cure gradient through a cross
section of the thickness of the material being cured. Typically,
the material to be cured is in the form of a sheet having a given
sheet thickness. Desirably, at least one of the dose-depth profile
calibration curves for the cured material exhibits a minimum within
a middle 80% of the thickness of the material, more desirably,
within a middle 50% of the thickness of the material. Further, at
least one of the dose-depth profile calibration curves for the
cured material exhibits a concave downward profile.
The exemplary method of making an adhesive article using a Minimum
Calculated Core Cure value of the material based on dose-depth
profile calibration curves for the electron beam generating
apparatus and for the material to be cured can be used to make an
adhesive article, such as the above-described adhesive article
comprising a blend of high and low molecular weight acrylic
copolymers. In one exemplary method, the material to be cured
comprises a blend of (1) the first acrylic copolymer and (2) the
second acrylic copolymer; wherein the pbw of monomer(s) D in the
second acrylic copolymer is greater than the pbw of monomer(s) B in
the first acrylic copolymer.
The present disclosure is also directed to methods of making
multi-layered articles comprising at least one adhesive core layer.
The adhesive core layer may be combined with one or more additional
layers using conventional techniques including, but not limited to,
lamination, coating, coextrusion, etc. Suitable additional layers
include layers described above.
In some embodiments, multi-layered adhesive articles are desirably
formed by co-extruding the above-described extrudable adhesive
composition containing first and second acrylic copolymers with one
or more extrudable polymer compositions. The number and type of
polymer compositions are selected based upon the desired properties
of the final adhesive article. For example, in the case of adhesive
core layers having relatively low tack at room temperature (for
example, the adhesive core layer is not a PSA), it may be desirable
to combine the adhesive core layer with one or more PSA
compositions to form an adhesive article having outer surface tack
at room temperature. Other examples of polymer compositions that
may be prepared by co-extrusion include, but are not limited to,
relatively high modulus polymer compositions for stiffening the
article (semi-crystalline polymers such as polyamides and
polyesters), relatively low modulus polymer compositions for
increasing the flexibility of the article (for example, plasticized
polyvinyl chloride), and additional foam compositions.
In one embodiment, the method of making multi-layered articles
comprises a coextrusion step wherein additional extrudable polymer
compositions are coextruded with the above-described extrudable
adhesive compositions. FIG. 3 illustrates one coextrusion process
for producing a multi-layered article comprising an adhesive core
layer sandwiched between a pair of additional layers. As shown in
FIG. 3, polymer resin is optionally added to a first extruder 30
(for example, a single screw extruder) where it is softened and
ground into particles. The resin particles are then fed to a second
extruder 32 (for example, a single or twin screw extruder) where
they are mixed with any desired additives. The resulting extrudable
composition is then metered to the appropriate chambers of die 14
through transfer tubing 34 using a gear pump 36. The resulting
article is a three-layer article featuring an adhesive core layer
having a polymer layer on each of its major surfaces (see, for
example, such a three-layer article in FIG. 1, namely exemplary
adhesive article 40).
It is also possible to conduct the co-extrusion process such that a
two-layer adhesive article is produced, or such that adhesive
articles having more than three layers (for example, 10-100 layers
or more) are produced by equipping die 14 with an appropriate feed
block, or by using a multi-vaned or multi-manifold die. Multilayer
adhesive articles can also be prepared by laminating additional
layers to the adhesive core layer, or to any of the co-extruded
polymer layers after the adhesive article exits die 14. Other
techniques which can be used include stripe coating.
Various adhesive articles of the present disclosure may be used in
a number of applications. As described above, the adhesive articles
may comprise a single adhesive core layer or may comprise one or
more layers in addition to an adhesive core layer. The adhesive
articles may be present in the form of a strip, tape, roll of tape,
or any other construction known in the art. The adhesive articles
may be bonded to one or more substrates to provide a multi-layered
article having a desired degree of contact between the adhesive
article and one or more substrates bonded thereto.
In some embodiments, the adhesive articles may be particularly
useful in a variety of applications, including aerospace,
automotive, and medical applications. The properties of the
adhesive articles may be tailored to meet the demands of the
desired applications. Specific examples of applications include,
but are not limited to, vibration damping articles, medical
dressings, tape backings, retroreflective sheet backings,
anti-fatigue mats, abrasive article backings, gaskets, and
sealants.
Various exemplary embodiments of the present disclosure are
described above and further illustrated below by way of examples,
which are not to be construed in any way as imposing limitations
upon the scope of the invention. On the contrary, it is to be
clearly understood that resort may be had to various other
embodiments, modifications, and equivalents thereof which, after
reading the description herein, may suggest themselves to those
skilled in the art without departing from the spirit of the present
invention and/or the scope of the appended claims.
EXAMPLES
These examples are merely for illustrative purposes only and are
not meant to be limiting on the scope of the appended claims. All
parts, percentages, ratios, etc. in the examples and the rest of
the specification are by weight unless indicated otherwise.
As used herein, a sheet generally refers to a sheet of material(s),
such as a foam sheet, that typically has a thickness of at least
about 5 mils. A film generally refers to a thinner sheet typically
having a thickness of about 5 mils or less. A tape generally refers
to a sheet that has been cut into a narrower width. In the
examples, the terms sheet, film and tape may be used
interchangeably.
Test Methods:
Gel Permation Chromatography (GPC)
Gel Permation Chromatography was used to determine the molecular
weights of the polymers. A sample of the resulting polymer was
removed from the package and Gel Permeation Chromotography was
performed on the sample according to the manufacturer's general
instructions and the following procedure to determine the molecular
weight. Three samples weighing approximately 25 milligrams (mg)
were tested for each of the polymers. Each sample was dissolved in
10.00 ml of tetrahydrofuran over a three day period, and then
filtered using a 0.25 micron Gelman PTFE syringe filter. A WATERS
Alliance 2695 Separations Module (available from Waters, Inc.
(Milford, Mass.)) was used to inject 100 microliters of each sample
solution into a two column set (available from Jordi Associates
Inc. (Bellingham, Mass.)). One column was equipped with a mixed bed
and the other with a 500 A column, both 25 cm). The WATERS 2695
chromatograph was operated at room temperature, using
tetrahydrofuran as the eluent, flowing at a rate of 1.0 ml/min. A
Shimadzu Scientific Inc. (Columbia, Md.) RID-10A refractive index
detector was used to detect changes in the concentration. The
molecular weight calculations were based on calibrations made of
narrow polystyrenes ranging in molecular weight from
7.50.times.10.sup.6 to 580.
Minimum Calculated Core Cure (MCCC)
The Minimum Calculated Core Cure (MCCC) was used as a measure of
the controlled amount of electron beam radiation delivered at
various depths through a thickness cross section of a specific
material, for example, a sheet or tape, having a specific
composition, thickness, and density. The electron beam dose at a
given accelerating voltage was plotted against thickness to obtain
a dose-depth profile having a minimum in approximately the center
portion of the cross section of the tape. Separate samples of each
tape construction were treated to a different dose and accelerating
voltage. The minimum cure in approximately the center of the core,
that is, the dose delivered to that part of the core, was
calculated for each tape and process conditions. The average cure
throughout the thickness of the tape was also calculated for an
Average Calculated Core Cure (ACCC). The samples were tested for
one or more desired end properties, for example, stress relaxation
and hanging shear strength in this case. Stress relaxation
expressed as the Stress Relaxation Ratio (SRR) was then plotted as
a function of the Minimum Calculated Core Cure. The SRR was also
plotted as a function of the product (Prod) of the ACCC and the
MCCC. The product provides somewhat more delineation of the values
in the plots and is consistent with the plot of just MCCC. Monte
Carlo code was used to help predict the depth and dose values based
on the apparatus and the tape construction, that is, the
composition, thickness, and density, to facilitate adjustment of
the electron beam dose at various depths to allow delivery of the
optimal dose to obtain the desired end product. This methodology is
described in U.S. Pat. No. 6,749,903, the subject matter of which
is hereby incorporated herein in its entirety.
The calculated cure depends on the specific equipment used to
deliver the electron beam, and those skilled in the art can define
a dose calibration model for the equipment used. For the examples
described herein, the radiation processing was performed on a Model
CB-300 electron beam generating apparatus (available from Energy
Sciences, Inc. (Wilmington, Mass.) equipped with a 0.076 mm (0.003
inch) thick, 30.48 cm (12 inch) wide polyester terephthalate
support film running through an inert chamber. A sample of a tape
with a liner on both sides was taped onto the support film and
conveyed at a speed of about 6.1 meters/min (20 feet/min) such that
the tape was treated from one side through the polyethylene release
liner. A thicker sample, such as a foam tape, may exhibit a cure
gradient through the cross section of the tape so that it is
desirable to expose the tape to electron beam radiation from both
sides. For the examples, the tape was treated from both sides by
turning the sample over after one pass through the machine and
conveying it through the machine again. This provided a controlled
dose to the central portion of the adhesive tape to effect
crosslinking and hence, temperature resistance. The oxygen level
within the chamber of the CB-300 was restricted to a range of 50 to
100 ppm. The standard nitrogen gap between the window and the web
path was 47 mm and the same machine settings were used on each pass
through the machine.
Prior to treating samples, the electron beam apparatus was
calibrated according to ASTM E 1818 with dosimetry using 10 micron
and 45 micron dosimeters, which are polymeric films containing
radiochromic dye, commercially available from Far West
Technologies, Inc. (Goleta, Calif.). The calibration provided a
measure of surface dose and a dose/depth profile as a function of
accelerating voltage and beam current. The actual sample dose is
the energy deposited into a square centimeter of substrate divided
by the density of the sample, so the dose-depth profile for
substrates having different densities than the dosimeters were
normalized. A dose-depth profile was calculated for each tape
construction (which typically has a liner, a foam core of a
specific composition, and optional skin layers of specific
compositions on the foam core) to account for the differences in
densities of the different layers that the electron beam must
penetrate to reach the center of the tape. Samples tested for
Stress Relaxation Ratio (SRR) were representative of the thickness
and density of the samples that received a specified dose at a
specified accelerating voltage. The thickness and density
measurements were typically made immediately adjacent to the area
from which the SRR measurements were made.
Stress Relaxation Ratio--G(300)/G(0.1)--(SRR)
The Stress Relaxation Ratio (G(300)/G(0.1) test was used to
characterize the time dependent behavior of an adhesive article,
for example, a tape sample, when a constant level of shear strain
is applied to a sample. The shear modulus of a sample was measured
at specific time intervals during the test. When the test was
completed, a ratio was calculated using the modulus at 300 seconds
divided by the modulus at 0.1 seconds (G(300)/G(0.1)). This "stress
ratio" provides an indication of a material's "firmness" (for
example, the material's response under load).
The Stress Relaxation Ratio (G(300)/G(0.1) test was performed using
an Advanced Rheometric Expansion System (ARES) (available from TA
Instruments (New Castle, Del.)) with a 25 mm Parallel Plate Test
Fixture. The rheometer was equipped with RSA Orchestrator software.
The tape sample was a circular disc having a diameter of 24.5 mm (1
inch) and a thickness of approximately 0.51 mm (20 mil). For
samples thinner than 0.51 mm, several layers may be laminated
together to provide the requisite thickness. The test was run at
70.degree. C. (+/-1.degree. C.) with a 1 mm gap and 25% strain. The
data was recorded on a chart of the modulus (G) over time
(seconds). The Stress Relaxation Ratio was calculated by dividing
the modulus (G) at 300 seconds by the modulus at 0.1 second.
Hanging Shear
The Hanging Shear test was used as an indication of a tape's
internal cohesive strength at elevated temperature. A sample of
tape measuring 2.54 cm by 1.27 cm was laminated to an etched
aluminum panel measuring 2.54 cm by 5.08 cm such that the tape
edges were coextensive with edges of the panels. The panel
overlapped 1.27 cm to cover the tape and the free ends of the
panels extended in opposite directions. One end of a panel was hung
on a rack in an oven set at 70.degree. C. with a 500 gram weight
hanging from the bottom of the end of the other panel so that the
tape sample was under shear stress. The time for the bottom panel
to release from the hanging panel was measured up to 10,000
minutes. Test results are reported as Pass, that is, the panels
were still adhered together after 10,000 minutes in the oven, or
Fail, that is, the bottom panel had pulled away from the top panel
in less than 10,000 minutes.
Pressure-Sensitive Adhesive Compositions
Packaged pressure-sensitive adhesive compositions were prepared
according to the method described in U.S. Pat. No. 5,804,610, the
subject matter of which is hereby incorporated herein in its
entirety, using the compositions and materials as listed below.
PSA-1--A pressure-sensitive adhesive (PSA) composition was prepared
by mixing 45 parts of IOA (isooctyl acrylate), 45 parts of BA
(butyl acrylate), 10 parts of AA (acrylic acid), 0.15 part 2,2
dimethoxy-2-phenylacetophenone (IRGACURE.TM. 651 available from
Ciba Specialty Chemicals Corp. (Tarrytown, N.Y.)), and 0.06 part of
IOTG (isooctyl thioglycolate). The composition was placed into
packages measuring approximately 10 cm by 5 cm by 0.5 cm thick as
described in U.S. Pat. No. 5,804,610, the subject matter of which
is hereby incorporated herein in its entirety. The packaging film
was a 0.0635 mm thick ethylene vinyl acetate copolymer film (VA-24
Film available from CT film (Dallas, Tex.)). The packages were
immersed in a water bath and simultaneously exposed to ultraviolet
radiation at an intensity of about 3.5 milliWatts per square
centimeter, and a total energy of about 1680 milliJoules per square
centimeter as measured in NIST units. The PSA included both the
polymer and the packaging film. The resulting polymer, that is,
without the packaging film, had a M.sub.w of about
5.75.times.10.sup.5 and a M.sub.n of about 1.98.times.10.sup.5 as
measured by the Gel Permeation Chromotography procedure described
above.
PSA-2--A PSA composition was prepared according to the procedure
above for PSA-1 except that the composition was 95 parts of 2-EHA
(2-ethylhexyl acrylate), 5 parts of AA, 0.15 part IRGACURE.TM. 651
photoinitiator, and 0.02 part of IOTG. The resulting polymer had in
a M.sub.W of about 5.54.times.10.sup.5 and a M.sub.n of about
1.48.times.10.sup.5 when measured according to the previously
described GPC procedure.
PSA-3--A PSA composition was prepared according to the procedure
for PSA-2 except for the following changes in the composition: 0.2
parts of IRGACURE.TM. 651 photoinitiator, 0.8 parts of IOTG, and
0.4 part of
octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate
(IRGANOX.TM. 1076 available from Ciba Specialty Chemicals Corp.)
was added. A total energy of about 4107 mJ per sq cm was used. The
resulting polymer had a M.sub.W of about 5.54.times.10.sup.4 and a
M.sub.n of about 2.84.times.10.sup.4.
PSA-4--A PSA composition was prepared according to the procedure
for PSA-3 except 0.3 parts of IOTG was used. A total energy of
about 4107 mJ per sq cm was used. The resulting polymer had a
M.sub.W of about 1.28.times.10.sup.5 and a M.sub.n of about
5.15.times.10.sup.4.
PSA-5--A PSA was prepared according to the procedure for PSA-3
except that 85 parts of 2-EHA and 15 parts of AA were used and the
total energy used was 1785 mJ per sq cm. The resulting polymer had
a M.sub.w of about 4.72.times.10.sup.4 and a M.sub.n of about
2.84.times.10.sup.4.
PSA-6--A PSA was prepared according to the procedure for PSA-5
except that 0.3 part of IOTG was used, and the total energy was
about 1778 mJ per sq cm. The resulting polymer had a M.sub.w of
about 8.86.times.10.sup.4 and a M.sub.n of about
5.72.times.10.sup.4
PSA-7--A PSA was prepared according to the procedure for PSA-3
except that 80 parts of 2-EHA and 20 parts of AA were used and the
total energy used was 1778 mJ per sq cm. The resulting polymer had
a M.sub.w of about 3.94.times.10.sup.4 and a M.sub.n of about
2.54.times.10.sup.4.
PSA-8--A PSA was prepared according to the procedure for PSA 5
except that 90 parts of 2-EHA, 10 parts of AA, and 0.03 part of
IOTG were used. The total energy used was about 1530 mJ per square
cm. The resulting polymer had a M.sub.w of about
5.75.times.10.sup.5 and a M.sub.n of about 1.98.times.10.sup.5.
Skin Adhesive-1 (SA-1)
Skin Adhesive-1 was prepared by feeding about 12.7 parts of a
thermoplastic rubber (KRATON D-1340K, a multi-arm block copolymer
with about 9% styrene, obtained from Kraton Polymers, Inc. (Houston
Tex.), and made according to U.S. Pat. No. 5,393,373, the subject
matter of which is hereby incorporated herein in its entirety) from
a K-tron.TM. weight loss feeder into Zone 1 of a 40 mm Berstorff
twin screw extruder having 10 heated zones set at 120.degree. C.
The screw had conveying sections in zones 1, 4, 8, 9, and 10, and
mixing sections in the later portions of Zones 2, 3, 5, 6, and 7.
Other components were fed into different zones of the extruder
using the feed equipment and temperatures as follows (all amounts
are approximate as there are variations in the feeding devices,
speed, etc.):
Zone 2: 6.2 parts of 2-ethylhexyl diphenyl phosphate plasticizer
(SANTICIZER 141 available from Ferro Co. (Bridgeport,
N.J.))--Zenith pump/hose with temperatures set at room
temperature.
Zone 3: 23.2 parts of an aliphatic C-5 tackifying resin (EXCOREZ
1310LC available from ExxonMobil Chemical LTD. (Southampton,
Hampshire, GB))--grid melter/melt pump/hose with temperatures set
at 160.degree. C.
Zone 4: 0.38 parts of black pigment having a 50/50 blend of carbon
black in ethylene vinyl acetate copolymer resin having a melt index
of about 150 (4900 CMB available from MA Hanna Color (Suwanee,
Ga.)) fed from a disc doser.
Zone 5: 53.1 parts of PSA-1-51 mm Bonnot single screw extruder/melt
pump/hose with temperatures set at 150.degree. C.
Zone 6: 3.8 parts of a stabilized rosin acid ester tackifying resin
(Superester W-115 available from Arakawa Chemical USA (Chicago,
Ill.)) mixed with 0.26 parts of
pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate
(IRGANOX 1010 antioxidant available from Ciba Specialty Chemical
Co.), and 0.26 parts of
2-(2-hydroxy-3,5-di-(tert)-amylphenyl)benzotriazole (TINUVIN 328
ultraviolet light absorber available from Ciba Special Chemicals
Co.)--grid melter/melt pump/hose with temperatures set at
160.degree. C. The compounded adhesive was collected in a box lined
with silicone release agent.
Skin Adhesive-2 (SA-2)
SA-2 was prepared according to the procedure for SA-1 except that
11.5 parts of thermoplastic rubber (KRATON D-1340K), 20 parts of
ESCOREZ 1310LC tackifier, 55.6 parts of PSA-1, 6 parts of
Superester W-115 tackifier, and 3 parts of SANTICIZER 141
plasticizer were used.
Example 1
A foam core composition was prepared by feeding 97.7 parts of PSA-3
into zone 1 of a 40 mm Berstorff twin screw extruder having
conveying sections in zones 1, 4, 8, and 9, and mixing sections in
the later portions of zones 2, 3, 5, and 6. The extruder had 10
heated zones, each set at 120.degree. C. PSA-2 was fed from a 51 mm
single screw extruder (Bonnot) apparatus having a melt pump and
hose with temperatures set at 121.degree. C./150.degree.
C./150.degree. C. respectively. A K-tron.TM. T20 feeder was used to
add 2.3 parts of expandable microspheres having a shell composition
containing acrylonitrile and methacrylonitrile and a core of
isopentane (DUALITE.TM. U010-185D expandable microspheres,
available from Sovereign Specialty Chemicals Inc. (Avon, Ohio)).
The microsphere-containing compounded core was fed through a melt
pump and hose, each set at about 150.degree. C., to the center port
of a 25.4 cm (10 inch) wide Cloeren three-layer adjustable vane
type die with a keyhole shaped manifold set at a temperature of
192.degree. C. The feed rate of the microspheres was adjusted to
achieve a particular target density.
A foam tape was prepared by feeding SA-1 (Skin Adhesive-1) at a
rate of about 2.63 kg/hour to the outer layer port of the 3-layer
Cloeren die from a 51 mm single screw extruder (Bonnot) with a melt
pump and hose set at temperatures of 150.degree. C. The die vanes
were adjusted to distribute the skin approximately equally to both
sides of the die lips. The foam core composition was fed to the
center layer at about 11.35 kg/hour. Upon exiting the die, the
co-extruded layers were cast onto a silicone release coated casting
roll having a diameter of 18 inches and operated at a surface speed
of about 1.37 meters/minute. The roll was cooled with water having
a temperature of about 12.degree. C. The cooled extrudate was
transferred from the casting roll to a 0.117 mm thick silicone
coated polyethylene release liner that was transported at the same
speed as the casting roll to the end of the web transport line
where it was cut into approximately 1.25 meter lengths. Another
sheet of the same release liner was hand laminated to each sheet
using a hand-held rubber roller to exclude trapped air, and the
sheets were stacked. The resulting foam tape had a total thickness
of about 1.14 mm as measured with a digital caliper and a density
of about 0.61 grams per cubic centimeter (g/cc). The skin adhesive
layers on either side of the core had a thickness of 0.076 mm
(0.003 inch) and a density of about 0.98 g/cc, and the core had a
thickness of about 0.99 mm (0.039 inch) and a density of about 0.98
g/cc. The liners each had a thickness of 0.117 mm (0.0046 inch) and
a density of 0.99 g/cc.
The tape was irradiated with electron beam radiation at an
accelerating voltage of 300 KeV and a dose of 10 megarads from one
side of the tape. A plot of dose against tape thickness is shown in
FIG. 4. The radiation was not sufficient to crosslink the tape on
the side of the tape opposite the E-beam.
The sample was turned over and a second pass was made through the
E-beam apparatus at the same accelerating voltage and dose. The
resulting plot is shown in FIG. 5. The additive effect of the
radiation in the middle of the tape was greater than at either
surface so the resulting plot was a convex curve.
The accelerating voltage was lowered to 230 KeV and a second sample
of the tape was run through the apparatus twice. The additive
effect of the radiation in the middle of the tape was less than at
either surface so the resulting plot had a concave downward profile
with the minimum within about the central third of the cross
section of the tape as shown in FIG. 6. The minimum, that is, the
MCCC (Minimum Calculated Core Cure), was correlated to the shear
strength and stress relaxation of the sample.
Five more samples of the same tape construction were treated with
different accelerating voltages and doses as shown in Table 1. The
stress relaxation and static shear strength were measured for each
process condition and the minimum e-beam cure in the cross section
was calculated according to the procedure for determining MCCC. The
average cure throughout the thickness of the tape was also
calculated. The product of the minimum core cure and the average
core cure (Product) was calculated. This product appears to provide
a better resolution of the data than just the minimum cure value
alone. The stress relaxation values were plotted against the MCCC
values for each dose as shown in FIG. 7. The stress relaxation was
also plotted against the product of the Average Calculated Core
Cure (ACCC) and the Minimum Calculated Core Cure (MCCC) as shown in
FIG. 8.
Monte Carlo code was used to help select the accelerating voltage
and dose for each sample. This example illustrates an exemplary
method of the present disclosure wherein the Minimum Calculated
Core Cure is used to adjust the treatment level to meet the
performance requirements of a particular tape composition (liner,
core, skin adhesives) and density.
Examples 2-8
Foam tapes were prepared according to the procedures described
below. Two to five samples of each tape construction were exposed
to different electron beam accelerating voltage in KeV and dose in
MRads as indicated by the letter after the Example number shown in
Table 1. Each sample was exposed to two passes through the
apparatus so that both sides of the tape were irradiated. An e-beam
dose/depth profile was calibrated for each cured sample according
to the procedure described above. The Minimum Calculated Core Cure
(MCCC) in megarads was determined as well as the Average Calculated
Core Cure (ACCC) in megarads and the Product of the MCCC and the
ACCC. Representative samples of the cured tape corresponding to
each accelerating voltage and dose were measured for thickness and
density, and tested for Shear Strength (SS) and Stress Relaxation
Ratio (SRR). Results are shown in Table 1. The Stress Relaxation
was plotted as a function of the Minimum Calculated Core Cure as
shown in FIG. 7. The Stress Relaxation Ratio (SRR) was also plotted
as a function of the Product of the Average Cure (Product) and the
Minimum Cure as shown in FIG. 8.
The data shows how the stress relaxation characteristics of tapes
having varying compositions can be controlled by the selection of
the appropriate dose and accelerating voltage on an electron beam
apparatus to provide the desired properties of the adhesive tape.
The e-beam conditions were selected to provide a desired shear
strength and stress relaxation characteristic so that a process
window can be established to make tapes of a given composition,
thickness, and density.
Example 2
A foam tape was prepared according to the procedure of Example 1
except as follows. The foam composition was prepared by feeding 84
parts of PSA-2 from the single screw extruder to the twin screw
extruder. A similar single screw extruder with temperatures set at
100.degree. C./100.degree. C./120.degree. C. was used to feed 13.7
parts of PSA-3 into zone 2 of the twin screw extruder. The casting
roll speed was about 1.25 m/min. The resulting foam tape had a
total thickness of about 1.1 mm, and a density of about 0.606
g/cc.
Example 3
A foam tape was prepared according to the procedure of Example 2
except that the single screw extruder was used to feed 13.7 parts
of PSA-4 into zone 2 of the twin screw extruder. The casting roll
speed was about 1.22 m/min. The resulting foam tape had a total
thickness of about 1.16 mm, and a density of about 0.623 g/cc.
Example 4
A foam tape was prepared according to the procedure of Example 2
except that the single screw extruder apparatus temperatures were
set at 93.degree. C./107.degree. C./120.degree. C., and about 13.7
parts of PSA-5 were fed into zone 2 of the twin screw extruder. The
casting roll speed was about 1.4 m/min. The resulting foam tape had
a total thickness of about 1.09 mm, and a density of about 0.623
g/cc.
Example 5
A foam tape was prepared according to the procedure of Example 4
except that about 13.7 parts of PSA-6 were fed into zone 2 of the
twin screw extruder. The casting roll speed was about 1.5 m/min.
The resulting foam tape had a total thickness of about 1.13 mm, and
a density of about 0.637 g/cc.
Example 6
A foam tape was prepared according to the procedure of Example 4
except that about 13.7 parts of PSA-7 were fed into zone 2 of the
twin screw extruder. The casting roll speed was about 1.58 m/min.
The resulting foam tape had a total thickness of about 1.19 mm, and
a density of about 0.635 g/cc.
Example 7
A foam tape was prepared according to the procedure of Example 2
except that about 83.2 parts of PSA-2 were fed into zone 1 of the
twin screw extruder, about 13.5 parts of PSA-5 were fed into zone
2, and about 3.3 parts of expandable microspheres were added to
zone 8. The casting roll speed was about 1.6 m/min. The resulting
foam tape had a total thickness of about 1.10 mm, and a density of
about 0.55 g/cc.
Example 8
A foam tape was prepared according to the procedure of Example 4
except that about 83.1 parts of PSA-8 were fed into zone 1 of the
twin screw extruder, 15 parts of PSA-5 were fed into zone 2, and
1.9 parts of expandable microspheres were added to zone 8. The
casting roll speed was about 1.3 m/min. The resulting foam tape had
a total thickness of about 1.14 mm, and a density of about 0.65
g/cc.
TABLE-US-00001 TABLE 1 Test Results Voltage-Dose Static Thickness
Density MCCC ACCC Product Ex Kev-Mrad Shear SRR mm g/cc Mrad Mrad
Mrad 1A 238-9 Fail 0.0906 44.8 0.6165 1.5 7.3 10.95 1B 240-10 Pass
0.1375 44.58 0.6065 2.5 8.3 20.75 1C 245-11 Pass 0.2073 44.77
0.6105 3.7 9.47 35.039 1D 250-11 Pass 0.265 44.8 0.61 5.3 9.86
52.258 1E 277-11 Pass 0.4046 45.7 0.6152 11 11.705 128.755 2A 238-9
Fail 0.0364 45.75 0.6052 1.7 7.336 12.4712 2B 240-10 Fail 0.0752
44.75 0.6046 2.5 8.3 20.75 2C 245-11 Fail 0.0961 46.5 0.604 3.6
9.443 33.9948 2D 260-11 Pass 0.2509 47.9 0.6089 6.5 10.38 67.47 2E
277-11 Pass 0.3444 47.75 0.6033 10.5 11.58 121.59 3A 238-9 Fail
0.0335 45.08 0.6213 1.6 7.309 11.6944 3B 240-10 Fail 0.0541 45.25
0.6213 2.1 8.242 17.3082 3C 245-11 Fail 0.119 45.48 0.6189 3.5
9.436 33.026 3D 260-11 Pass 0.2454 46.52 0.625 6.5 10.392 67.548 3E
277-11 Pass 0.3329 46.5 0.6264 10.3 11.524 118.6972 4A 238-9 Fail
0.0500 41.52 0.62 2.5 7.42 18.55 4B 240-10 Fail 0.0530 44.08 0.626
2.1 8.19 17.199 4C 250-11 Pass 0.1300 44.1 0.626 4.9 9.84 48.216 4D
264-11 Pass 0.18434 42.5 0.623 9 11 99 4E 277-11 Pass 0.23313 42.72
0.62 11.8 11.93 140.774 5A 238-9 Fail 0.0293 44.55 0.6384 1.1 7.18
7.898 5B 240-10 Fail 0.0468 44.65 0.6372 1.7 8.11 13.787 5C 258-10
Pass 0.15143 44.5 0.633 5.8 9.33 54.114 5D 273-10 Pass 0.20871 44.1
0.6385 8.69 10.31 89.5939 5E 277-11 Pass 0.2599 44.45 0.6317 10.7
11.6 124.12 6A 240-10 Fail 0.0322 47.27 0.6411 0.8 7.95 6.36 6B
258-10 Fail 0.08763 46.8 0.635 4.5 9.16 41.22 6C 273-10 Pass
0.17505 44.05 0.6385 8.9 10.31 91.759 6D 277-11 Pass 0.1767 47.07
0.6355 9.3 11.26 104.718 7A 228-9 Fail 0.11017 37 0.5408 4.1 7.6
31.16 7B 236-10 Pass 0.16567 35.9 0.5297 7.4 9.3 68.82 8A 250-9
Pass 0.10156 45.05 0.6615 2.7 7.77 20.979 8B 260-9 Pass 0.11692
44.55 0.6625 4.8 8.36 40.128 8C 278-8.5 Pass 0.13335 45.5 0.6320 8
8.9 71.2
While the specification has been described in detail with respect
to specific embodiments thereof, it will be appreciated that those
skilled in the art, upon attaining an understanding of the
foregoing, may readily conceive of alterations to, variations of,
and equivalents to these embodiments. Accordingly, the scope of the
present invention should be assessed as that of the appended claims
and any equivalents thereto.
* * * * *